In current passenger aircraft, cold ambient air on one hand and hot exhaust air from a so-called bleed air system of an aircraft engine on the other hand are used for air conditioning of the cabin. Ambient air is fed into an aircraft cabin for the fresh air supply of the passengers and for temperature control of the aircraft cabin. The cool fresh air is mixed with the hot bleed air in a mixing chamber, thus temperature-controlled, and distributed in the aircraft cabin.
To meet corresponding cooling requirements, ambient air or air-conditioned air having a temperature approximately below the 0° C. boundary is frequently used in aircraft air conditioners. Because of this cold temperature below the freezing point and the simultaneous presence of free water and/or ambient humidity, icing of the downstream pipelines and the installed devices or valve may occur, if they come into contact with the cold air, which contains water. This may interfere with the function of check valves, cause damage to valves, and cause the breakdown of corresponding devices or possibly damage to pipelines, for example. It has been shown that the icing is especially critical in a temperature range from approximately −8° C. to 0° C., because crystals may frequently form due to the relatively high proportion of free water.
Various regulating algorithms are known, which are to prevent icing and/or are to remove existing icing (anti-ice control). Thus, for example, the possibility exists of heating the temperature of the air-conditioning outlet air cyclically (i.e., temporarily, significantly above the 0° C. limit within a predefined period of time to thus remove possibly existing ice or ice particles in the air conditioner outlet pipeline and/or the devices installed therein, such as sensors, check valves, etc.).
In a broad regulating algorithm, the temperature of the air conditioner outlet air is kept continuously above the 0° C. limit. Icing may be prevented in this way, so that no ice or ice particles may form in the air conditioner outlet pipeline and/or devices installed therein. When a temperature over 0° C. is maintained, reduced cooling capacity occurs. The dependence of the temperature difference (dT) is clear on the basis of the formula Q=m×dT×cp. This has a linear effect on a total cooling capacity (Q) of the air conditioner.
The total cooling capacity of the air conditioner is significantly reduced by the cyclic heating of the air-conditioning outlet temperature or permanently maintaining the temperature at significantly above 0° C. Sufficient cooling capacity may thus no longer be applied upon mixing with the hot bleed air in the mixing chamber, so that the cabin temperature of the aircraft cabin increases, which reduces the cabin comfort.
In a further regulating algorithm, the critical range from approximately −8° C. to 0° C. may be left out and/or passed rapidly by special regulation of the air conditioner outlet temperature. The air conditioners deliver hot air above approximately 0° C. and cold air below approximately −8° C. cyclically, which is mixed later in a mixing chamber. By leaving out the critical temperature range, nearly no ice or ice particles form in the air conditioner outlet pipe and/or the devices installed therein. These air conditioners which do not drive and/or pass rapidly through the critical area from approximately −8° C. to 0° C. have a smaller risk of ice formation and/or ice particle formation in the air conditioner outlet pipelines and/or the devices installed therein.
However, temperature oscillations arise in the cabin due to this rapid passage through the critical temperature range and the cyclically varying air supply at different temperatures, so that a continuous temperature change is detectable in the cabin. This results in reduced cabin comfort. Because of the regulation to a low air conditioner outlet temperature, the air conditioner delivers higher cooling capacity than is needed in the aircraft cabin for cooling. Because of the cold air conditioner outlet temperature of the air conditioner, it must be heated in a complex and costly way, for example, via powerplant air, auxiliary powerplant air, or so-called ground carts. The overall efficiency of the air conditioner is thus reduced.
Among other things, it at least one object of the present invention to reduce the icing danger in air conditioners for aircraft. In addition, other objects, desirable features, and characteristics will become apparent from the subsequent summary and detailed description, and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.